Various heavy metals having a high economic value, such as gold, silver and platinum, are often found in particle or flake form in a deposit of earthen material. In order to extract the valuable metals from the remaining surrounding waste earth material, there have been numerous prior art developments used.
The desired heavy metals are generally found in what are termed placer deposits, which normally occur through the process of weathering and erosion. Placer deposits are generally found in or around the beds of existing streams and rivers, or in or along the beds of ancient streams and rivers.
Most of the separation devices and methods involve the use of water because of its properties with respect to separating and breaking up particles of earthen material.
Very often the placer deposits in which the valuable heavy metals are found are small, and particularly in the present day are very remote from such things as roads and electrical power. Because of this, it is desirable that a heavy metal separator be portable and require a minimal amount of electrical power to operate, so that a small portable generator can be utilized with it.
One of the earlier and most simple of the separation methods involve the use of what is commonly known as a "gold pan". The earth material containing the desired heavy metals was placed into the pan along with an amount of water. Through a combination of circular and rocking motions, the waste earth material was eventually washed out of the gold pan, leaving the desired heavy metals in the pan. The disadvantage inherent in the use of a gold pan is that it is very slow, and only a small volume of material can be processed at one time.
Other prior art methods included such devices as riffle beds, shaker tables, jigs, sluice boxes, and combinations of the above.
Another method of separating heavy metals from waste material utilizes an apparatus which directs a descending stream of heavy metal and earthen material into an ascending stream of water, with the water forcing the lighter waste material up and out of the apparatus while at the same time allowing the heavy metal to settle to the bottom of the apparatus for collection.
An example of this latter type of apparatus is shown in U.S. Pat. No. 4,101,419 to Bergman. In the Bergman patent, a cone shaped chamber has a plastic tube at the bottom with a water inlet near the bottom of the cone shaped chamber. The earthen material with the heavy metal particles included is placed into the cone shaped chamber, and an upwardly moving stream of water is introduced into the bottom of the cone. Even though the volume of the water entering the cone is very low, with low head pressure, the apparatus is supposed to wash waste material out of the top of the cone and allow heavy metal particles to settle to the bottom.
With the Bergman apparatus, if there is much variation in the size of the waste particles and heavy metal particles, a large number of waste material particles will also settle to the bottom, since the larger waste particles will weigh as much or more than the smaller heavy metal particles and will settle to the bottom of the cone.
In order to alleviate this problem, the Bergman apparatus also includes a screen which is positioned at the top of the cone. The material to be separated is placed in the screen which is manually agitated to facilitate the passage of the finer material through the screen downward into the cone, thence to be separated into heavy metal particles and waste material.
While the apparatus shown in the Bergman reference is easily transportable, it has several disadvantages. The first of these is that in order to obtain any initial size separation with the screen, the screen must be manually agitated and must be positioned below the level of water in the cone in order to separate the finer material from the coarser material. The screen must be physically removed and the coarse material emptied from the screen when it becomes filled. The separation process can then be restarted, with the coarser material being introduced into the cone. This, however, necessitates an adjustment of the volume of water which is flowing into the cone. Because of the low water pressure which is introduced into the cone, a lot of waste material will enter into the bottom of the cone along with the heavy metal particles.
Another apparatus for separating ores is shown in U.S. Pat. No. 1,961,666 to Hoyois. The Hoyois reference discloses a horizontal trough with at least one opening in the bottom of the trough which is in communication with a chamber underneath the trough. An upwardly flowing stream of water moves through the chamber. The most dense particles settle downwardly through the opening in the trough and through the chamber. The dense particles pass through the upwardly moving stream of water into the bottom of the chamber, where they are collected and removed. The remaining material is washed out the top of the chamber. In actual practice, a series of chambers are normally disposed below the trough, with successively smaller groups of particles initially passing from the trough into each of the successive chambers. The material washed from one chamber is washed into the next, and so on.
There are several disadvantages to the Hoyois apparatus. The first is that it is designed to handle material with particle sizes ranging from 20 to 80 millimeters, which means the apparatus will be fairly large. This makes the system essentially nontransportable. A second disadvantage is that material is collected at the bottom of each of the individual separation chambers. This means that there must be a method of conveying the waste material from each of the separation chambers. In addition, if this apparatus were used in an attempt to settle heavy metal particles from a stream of material passing over the trough, waste particles which were of the same approximate weight as the heavy metal particles passing through each of the various openings into the bottoms of the successive separation chambers would also pass downwardly through the separation chambers and be mixed with the desired heavy metal particles at the bottom of the chambers.
None of the prior art systems provide a transportable and easily usable heavy metal separation device which can handle a relatively large volume of ore concentrates in an essentially automatic manner, and ensure a very high recovery rate of the desired heavy metal particles from the ore concentrates.